The Clean Air Amendment of 1970, which established exhaust emission standards for 1975 and 1976 in light duty vehicles (passenger cars and light trucks), requires that the emissions of carbon monoxide and unburned hydrocarbons be reduced by at least 90 percent, as compared with 1970 emission control standards. Also the emissions of oxides of nitrogen from light duty engines are required to be at least 90 percent below the average of those actually measured from similar vehicles manufactured during the model year 1971. The 1975 standards for cars and light trucks are:
0.41 grams per vehicle mile for hydrocarbons (HC); PA1 3.4 grams per vehicle mile for carbon monoxide (CO); and PA1 3.1 grams per vehicle mile for oxides of nitrogen (NO.sub.x). PA1 The 1976 model year standards are: PA1 0.41 grams per vehicle mile for hydrocarbons; PA1 3.4 grams per vehicle mile for carbon monoxide; and PA1 0.4 grams per vehicle mile for oxides of nitrogen.
The Clean Air Amendments also require vehicle compliance with the above standards for five years or 50,000 miles, whichever occurs first.
United States and foreign automobile manufacturers have begun developing various prototype emission control systems which will meet the 1975 standards. These emission control systems have included so-called engine "add on" devices such as:
(1) An exhaust-gas recycle (EGR) line and control valve designed to recycle about 10 percent of the exhaust flow to hold NO.sub.x emissions below 3 grams per mile.
(2) A catalytic converter in the exhaust system to promote further oxidation of the HC and CO emissions from the engine; and
(3) A thermal reactor within the exhaust system to promote further burning of HC and CO emissions prior to exhaust into the atmosphere.
Each of these systems has disadvantages. The exhaust gas recycling systems currently in use generally cause a loss of engine power due to a reduction of available air-fuel ratio variations required for smooth engine operation. The use of EGR requires fuel mixture enrichment to maintain adequate drivability which results in an appreciable fuel economy penalty.
Catalytic converters currently being developed require the use of oxidation catalysts comprising nobel metals such as platinum and/or palladium or base metals promoted with noble metals deposited on both monolythic and pellet substrates within the engine exhaust system.
These catalytic systems have thus far demonstrated very poor durability and high cost - both in terms of initial component expense and fuel economy loss.
Thermal reactors, thus far developed, have required either fuel rich or fuel lean mixtures which have resulted in either substantially poor fuel economy (in the case of fuel rich mixture) or poor drivability (in the case of fuel lean mixtures).
Among alternate approaches to the "add on" emission control devices is a carbureted stratified charge engine. A prototype of this engine has been developed by Honda of Japan. The engine uses a conventional engine block, pistons and spark plugs. The cylinder head, however, is modified to comprise a small pre-combustion chamber which is in communication with a main combustion chamber. The spark plug is in the small pre-combustion chamber which is fed with a fuel rich mixture through a separate carburetor and by using a small third poppet valve. The main carburetor intake system feeds a fuel-lean mixture to the normal intake valve adjacent the main combustion chamber.
The fuel-rich mixture insures good ignition within the pre-combustion chamber. This mixture exits the pre-chamber and propagates a flame into the fuel-lean mixture in the main chamber to produce a burn of relatively long and uniform duration which reduces NO.sub.x formation and promotes total combustion of HC and CO inside the cylinder on the power stroke of the piston.
The Honda engine has been tested and has met the above 1975 standards without the addition of any "add on" emission control devices. It is apparent from the test results thus far published that the carbureted stratified charge engine offers several advantages over the alternate developments devised to meet the Clean Air Act standards, namely:
(1) No exhaust treatment need be used in conjunction with the engine;
(2) The engine is durable; the 1975 standards have readily been met after completion of the 50,000 mile durability testing as prescribed under the Clean Air Amendment;
(3) Effects on vehicle performance are small; there is a slight loss in power for comparable engine displacement due to leaner operation and decreased volumetric efficiency. Fuel economy, as compared with non-stratified charge engines, is essentially unchanged with no fuel penalty resulting from the lowered emissions output; and
(4) The engine can operate on regular leaded gasoline, unlike systems having catalytic converters for which lead is a catalyst poison.
Although the stratified charge principle is demonstrably advantageous - both from a clean air and fuel economy aspect - currently existing prototypes which have been tested are even more complex than conventional automotive engines. First, the disclosed engines have a third poppet valve which must be timed in conjunction with engine intake. Second, these stratified charge engines require two separate carburetors having two mechanically linked throttle plates and two separate intake manifolds.
From the standpoints of production cost and post-production maintenance, it is believed that the additional complexity of the currently proposed stratified charge engines will prevent most of them from being readily mass produced in the near future.
The present invention is directed to a simplified apparatus for applying a stratified charge to an engine which eliminates the necessity of separate carburetion apparatus and multiple poppet valves per cylinder. The system comprises a rotary valve in combination with a novel bifurcated intake manifold which eliminates the need for any reciprocating valves, valve springs or cam shafts. It is believed that the present invention provides a stratified charge engine which will meet the Clean Air Act requirements, supra, without attendant manufacturing or maintenance difficulties which are present in even conventional automobile engines on the market.